Two-stroke internal combustion engines

ABSTRACT

The specification discloses a two cylinder two stroke engine in which the cylinders are arranged in V-formation. The cylinders contain pistons connected to a crankshaft located in a crankcase and fuel-air mixture in pre-compressed in the crankcase prior to admission to the cylinders. The crankcase is divided into two separate pre-compression chambers, are for each cylinder, by a sealing disc rotatably mounted on the crankshaft and in sealing engagement around its periphery with the crankcase.

United States Patent Pirault 1 Nov. 13, 1973 [5 TWO-STROKE INTERNALCOMBUSTION 1,336,232 4/1920 Isliker 123/73 A ENGINES 2,265,677 12 1941Straub 123/55 R [75] Inventor: Jean-Pierre Pirault, Maidenhead,

g and Primary Examiner-Laurence M. Goodridge [73] Assignee: VandervellProducts Limited, Assistant g z g g f Tom Maidenhead, Berkshire, Englandaw [22] Filed: Feb. 25, 1972 [21] Appl. No.: 229,317 [57] ABSTRACT Thespecification discloses a two cylinder two stroke [30] ForeignApplicam": Priority Data engine in which the cylinders are arranged inV- May 26, 1971 Great Bfllaln 17,305/71 f ti The ylinderscontain pistonsconnected to a crankshaft located in a crankcase and fuel-air mix- Us.Cl. R, A t r i pre compressed in the crankcase prior to ad- [51] Int.Cl. F02b 33/04 mission to the cylinders The crankcase is divided into[58] Field of Search 123/73 R1 73 73 two separate pre-compressionchambers, are for each 123/73 197 A 55 57 56 56 B cylinder, by a sealingdisc rotatably mounted on the crankshaft and in sealing engagementaround its pe- [56] References Cited riphery with the crankcase.

UNITED STATES PATENTS 11/1910 Akerman 123/56 BA 7 Claims, 3 DrawingFigures TWO-STROKE INTERNAL COMBUSTION ENGINES BACKGROUND OF THEINVENTION This invention relates to two-stroke internal combustionengines of the kind having at least two mutually angled cylinderscontaining pistons, a crankcase in which mixture is compressed beforeadmission to the cylinders for combustion, and a crankshaft in thecrankcase to which the pistons are connected.

It is usual in engines of the above kind to connect the pistons toseparate crank pins of the crankshaft and to support the crankshaft in amain bearing between the crank pins. Thus the main bearing separates thecrankcase into two chambers, one for each cylinder, in which mixture ispre-compressed prior to admission to the cylinders.

It is a disadvantage of this construction that the length of the enginehas to be increased to accommodate the main bearing for supporting thecrankshaft between the crank pins.

SUMMARY OF THE INVENTION The invention provides a two-stroke internalcombustion engine having at least two mutually angled cylinderscontaining pistons, a crankcase in which mixture is compressed beforeadmission to the cylinders for combustion, and a crankshaft in thecrankcase to which the pistons are connected characterised in that thetwo pistons are connected to a common crankpin of the crankshaft, a discis rotatably mounted on the crank pin between the two connectionsandmeans are provided for sealing the periphery of the disc to thecrankcase and permitting relative rotation of the disc with thecrankshaft about the axis of the crankshaft with respect to thecrankcase.

It will be appreciated that the arrangement referred to above obviatesthe necessity of a main bearing supporting the crankshaft between theconnections of the two pistons to the crankshaft to provide a sealbetween the portions of the crank casing in communication with the twocylinders.

Said sealing means may comprise an annular inwardly facing channelaround the crankcase in which the periphery of the disc engages and thedisc may be arranged to be axially slidable on the crankshaft betweenthe connections to the pistons so that the periphery of the disc maysealably engage one or the other side of the annular channel accordingto the difference in pressure in the crankcase on either side of thedisc.

The outer periphery of the disc and the inner periphery of the discaround the crankshaft may be formed from a polymeric material.

In the latter arrangement the whole disc may be formed from polymericmaterial.

Alternatively the remainder of the disc may be formed from metal.

The polymeric material oroethylene.

Preferably the cylinders of the engine are arranged in V-formation.

The engine may have several cylinders in which case each pair of pistonsis connected to a common crankpin of the crankshaft and a disc isprovided on the crankpin between each pair of connections.

may be polytetraflu- BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is apart-section, part-elevation view through a two-stroke internalcombustion engine;

FIG. 2 is a view looking in the direction of the arrow A on FIG. 1; and

FIG. 3 is a detailed view of part of the crankshaft of the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawings shows a Vtwin twostroke engine having mutually inclined cylinders 10 and 11containing pistons 12 and 13. The cylinders are connected to a commoncrankcase 14 in which a crankshaft 15 is rotatably mounted. The pistons1 2, 13 are connected by connecting rods 16, 17 respectively to a commoncrankpin 18 of the crankshaft. A metal disc 19 is rotatably mounted onthe crankpin 18 between the connecting rods 16, 17 and the periphery ofthe disc engages in an annular channel 20 formed around the crankcase.The outer periphery of the disc is coated with polytetrafluoroethyleneas indicated at and the inner periphery of the disc is also coated withpolytetrafluoroethylene as indicated at 19b. As best seen in FIG. 3 ofthe drawings there is limited clearance indicated at 21 between the disc19 and crankpin 18 to permit the disc to slide along the crankpin 18 forthe purpose described below. The disc 19 divided the crankcase 14 intotwo compartments in communication with the cylinders 10, 11 respectivelybelow the pistons 12, 13. Fuel air mixture is drawn into the chambers insuccession as the pistons 12, 13 rise in their respective cylinders andis then compressed as the pistons fall and are delivered into thecombustion chambers above the pistons through passageways 22, 23 cut inthe cylinder walls 10, 11 respectively.

Since the cylinders 10, 11 are arranged in V- formation the pistons 12,13 will be out of phase with one another so that the pressure cycles inthe mixture on either side of the disc will also be out of phase withone another. Thus the disc 19 will be forced along the crankpin 18 toseal with one side of the annular channel 20 or the opposite sideaccording to which of the chambers is at the highest pressure.

It will be appreciated that this arrangement obviates the necessity of aseparate main bearing for the crankshaft between the connections of thepistons 12, 13 to the crankshaft so that the engine can be made shorterthan would have been possible than if an additional main bearing hadbeen used.

Although the engine described above has only two cylinders the inventionis equally applicable to engines having three or more cylinders in whichcase at least one pair and preferably each pair of pistons is connectedto a common crankpin in the crankshaft and a disc is provided on thecrankshaft between each pair of connections. I claim:

1. A two strgke internal cornbustion engine having at least two mutuallyangled cylinders 'cd'iiaifiifigisis tons, a crank case in which mixtureis compressed before admission to the cylinders for combustion, a crankshaft located in the crank case, said crank shaft having a crank pin towhich both said pistons are connected, a disc rotatably mounted on andaxially slidable along said crank pin between said connections, andmeans to seal the periphery of the disc with the crank case comprisingan annular inwardly facing channel encircling the crank case, saidperiphery of the disc engaging in the channel whereby a difference inpressure on either side of the disc forces the periphery of the discagainst one or the other side of the channel to form a seal therewith.

2. An engine as claimed in claim 1 wherein at least the outer peripheryof the disc and the iner periphery of the disc around the crankshaft areformed from a polymeric material.

3. An engine as claimed in claim 2 wherein the whole disc is formed fromthe polymeric material.

4. An engine as claimed in claim 2 wherein the remainder of the disc isformed from metal.

5. An engine as claimed in claim 2 wherein the polymeric material ispolytetrafluoroethylene.

6. An engine as claimed in claim 1 wherein cylinders of the engine arearranged in V-formation.

7. A two stroke internal combustion engine having at least two mutuallyangled cylinders containing pistons, a crank case in which mixture iscompressed before admission to the cylinders for combustion, a crankshaft located in the crank case, said crank shaft having a crank pin towhich both said pistons are connected, a disc rotatably mounted on andaxially slidable along the crank pin between said connections and meansto seal the periphery of the disc to the crank case while permitting thedisc to rotate with the crank pin with respect to the crank shaft.

1. A two stroke internal combustion engine having at least two mutuallyangled cylinders containing pistons, a crank case in which mixture iscompressed before admission to the cylinders for combustion, a crankshaft located in the crank case, said crank shaft having a crank pin towhich both said pistons are connected, a disc rotatably mounted on andaxially slidable along said crank pin between said connections, andmeans to seal the periphery of the disc with the crank case comprisingan annular inwardly facing channel encircling the crank case, saidperiphery of the disc engaging in the channel whereby a difference inpressure on either side of the disc forces the periphery of the discagainst one or the other side of the channel to form a seal therewith.2. An engine as claimed in claim 1 wherein at least the outer peripheryof the disc and the iner periphery of the disc around the crankshaft areformed from a polymeric material.
 3. An engine as claimed in claim 2wherein the whole disc is formed from the polymeric material.
 4. Anengine as claimed in claim 2 wherein the remainder of the disc is formedfrom metal.
 5. An engine as claimed in claim 2 wherein the polymericmaterial is polytetrafluoroethylene.
 6. An engine as claimed in claim 1wherein cylinders of the engine are arranged in V-formation.
 7. A twostroke internal combustion engine having at least two mutually angledcylinders containing pistons, a crank case in which mixture iscompressed before admission to the cylinders for combustion, a crankshaft located in the crank case, said crank shaft having a crank pin towhich both said pistons are connected, a disc rotatably mounted on andaxially slidable along the crank pin between said connections and meansto seal the periphery of the disc to the crank case whilst permittingthe disc to rotate with respect to the crank case.